1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a lamp assembly for a liquid crystal display device and a method of assembling the same.
2. Description of the Related Art
Generally, a liquid crystal display device (LCD) may be defined as a flat display device for displaying characters, images and/or moving pictures by precisely controlling liquid crystal in accordance with data processed at an information process device. A typical liquid crystal display device includes liquid crystal, a device for generating electric field, and a light supplying device.
The liquid crystal sensitively responds to changes in the intensity of the electric field, the device for generating electric field has a structure to precisely control the liquid crystal, and the light supplying device provides light which passes through the controlled liquid crystal.
The liquid crystal, the device for generating electric field, and the light supplying device are important components for a liquid crystal display device. The liquid crystal display device cannot properly operate when any of those devices does not accurately operate. For instance, the liquid crystal display device cannot properly operate when the light supplying device improperly operate although the liquid crystal and the device for generating the electric field properly operate.
The light supplying device includes a lamp for generating light, and a group of optical sheets for uniformly adjusting brightness of the light generated from the lamp. The light supplying device is called a lamp assembly.
It is desirable that a lamp emits white light such as the solar light and has planar light source optical distribution. Such a lamp, however, can be hardly manufactured so that lamps having linear light source optical distribution are widely used.
FIG. 1 is a schematic cross-sectional view illustrating a conventional lamp 10 having linear light source optical distribution.
Referring to FIG. 1, the lamp 10 has a transparent lamp tube 1, fluorescent material (not shown) coated on the inside wall of the lamp tube 1, discharging gas 2 injected into the lamp tube 1, and two electrodes 3 and 4 disposed on both end portions of the lamp tube 1.
A discharging voltage is externally applied to both electrodes 3 and 4 of the lamp 10. As a result, electrons 5 move from one of the electrodes 3 and 4 to the other of the electrodes 3 and 4 according to an electric potential difference between the electrodes 3 and 4. The electrons 5 collide with the discharging gas 2 while the electrons 5 move from one electrode to the other electrode. Hence, the discharging gas 2 is dissociated into discharging gas atoms, electrons and neutrons to form plasma. Light 6 having a predetermined wave length is generated during the dissociation of the discharging gas, and then excites the fluorescent material to generate visible light 7 from the fluorescent material. The supply of the discharging voltage to the lamp 10 is carried out using an inverter (not shown) and a transformer (not shown).
Recently, there has been a rapid development in the technology for a liquid crystal display device having a large display size, which is generally larger than that of a liquid crystal display device employing one lamp such as shown in FIG. 1. When the size of a display device is so large that one lamp cannot sufficiently illuminate a display region of the display device, the length of the lamp should be increased.
However, when the length of the lamp 10 is increased, the discharging voltage should be increased since the distance between the electrodes 3 and 4 is increased. In this case, a transformer should boost the voltage to increase the discharging voltage. As a result, power consumption of the display device is greatly increased.
To solve the power consumption problem, a multi-lamp type light source including multiple lamps connected to an inverter has been developed.
FIG. 2 is a schematic diagram showing a conventional multi-lamp type light source in which lamps are connected to one inverter, and FIG. 3 is a schematic diagram for illustrating brightness degradation of an image displayed by a display device including the lamps and the inverter in FIG. 2.
Power consumption of a display device employing the multi-lamp type light source does not increase because the lamps 20, 30 and 40 are connected to the inverter 50 in parallel. However, the multi-lamp type light source may cause brightness non-uniformity in an effective display region 70 where an image is displayed as shown in FIG. 3. The effective display region 70 can be defined as a maximum screen area which displays an image.
In this case, the brightness non-uniformity in the effective display region 70 may be caused by the reasons as follows.
The brightness non-uniformity occurs because the lamps 20, 30 and 40 are linear light source type. Such a problem can be overcome using a brightness correction device such as a light guiding plate.
Also, the brightness non-uniformity occurs due to electric current characteristic differences among the several lamps 20, 30 and 40 of the linear light source type as well as electric power supplied from the inverter 50.
Particularly, in the multi-lamp light source as shown in FIG. 2, plasma density in the lamps 20, 30 and 40 increases as the applied electric current increases when the lamps 20, 30 and 40 each generate light by means of forming plasma therein. The plasma density is increased, when a larger amount of electric current is applied thereto. That is, the lamps 20, 30 and 40 have electrical characteristics similar to a variable resistor whose resistance decreases in accordance with an increase in the electric current.
When the lamps 20, 30 and 40 are connected to one inverter 50 in parallel, the same electric power is applied to the respective lamps 20, 30 and 40. Thus, the lamps 20, 30 and 40 each emit light of the same luminosity if the electrical characteristics of the lamps 20, 30 and 40 are substantially identical.
However, since it is impracticable that all the lamps 20, 30 and 30 have the same electrical characteristics, a lamp having relatively better electrical characteristic is gradually brightened due to an increase of the applied current while a lamp having relatively poor electrical characteristic is gradually darkened due to a decrease of the applied current.
Therefore, the brightness differences among the lamps increase when a plurality of lamps are connected to one inverter providing electric power. Such problem can be overcome by connecting one inverter with one lamp. However, dimension and manufacturing cost of a display device are greatly increased when each lamp is provided with an inverter.